1. Field of the Invention
The present invention relates generally to apparatus for providing a measure of the distance between the apparatus and an object, and to such apparatus when coupled with primary optical means to cause the latter automatically to keep an image of the object, which is produced on an image plane by the optical means, in focus on that plane for a range of object distances. Specifically, the invention relates to the so-called spatial image correlation type or form of such apparatus, wherein the object distance is determined by relatively moving auxiliary image-producing auxiliary optical means and radiation responsive arrays until they occupy a critical or correlation position, this position being a measure of the existing object distance.
2. Description of the Prior Art
Distance determining and automatic focusing arrangements of the spatial image correlation type noted above have been proposed in the past. In each of these arrangements, the auxiliary optical means and the radiation responsive arrays, or detector arrays, are moved relatively, for each distance measuring or focusing operation, until there is best correspondence between the radiation distributions of the two auxiliary or detection images which the auxiliary optical means form on respective ones of the arrays. This condition of best distribution correspondence is identifiable by its production of a unique value or predetermined effect in the processed electrical output signal derived from the output signals of the elements which make up the arrays. For convenience, the said relative movement is generally achieved by moving or positioning a portion or member of the auxiliary optical means, such as a lens or a mirror, relative to the corresponding one of the arrays.
The particular position of the moved auxiliary optical member, in its range of movement, which yields the said best distribution correspondence and predetermined output signal effect is referred to as the correlation position for the existing object distance, and is unique to that distance. Accordingly, there is a correlation position of the moved auxiliary optical member for each object distance within the operating range of the apparatus. Thus, the recognition or detection of these correlation positions provides a measure, representation, or indication of the object distance.
Where the automatic focusing of a primary optical means, such as a camera taking lens, is effected by the apparatus just described, this means is moved and positioned along with the auxiliary optical means, the coupling between these two means being such that, when they are in the correlation position, the primary image of the object produced by the primary optical means is in best focus on an image plane.
Examples of different forms of arrangements of the type described above are found in the above-listed copending Stauffer application, in the Stauffer U.S. Pat. Nos. 3,836,772 and 3,838,275, and in the Biedermann et al. U.S. Pat. No. 3,274,914. In the Stauffer arrangements, an auxiliary lens or mirror and a primary lens coupled thereto are moved together, each time that the object distance changes, from a former correlation and focus position for the old object distance to a new correlation and focus position for the new object distance. In the Biedermann et al. form of apparatus, an auxiliary mirror and a coupled primary lens are moved together, each time that a focusing operation is initiated, from a datum position (the infinity focus position of the lens) to the position in which image correlation is achieved for the existing object distance. Subsequently, the mirror and lens are moved back to the datum position, ready for the next focusing operation.
Although the known apparatus, exemplified by the arrangements just described, doubtless has practical utility for certain applications, it is nevertheless characterized by certain shortcomings. Specifically, the Biedermann et al. type of apparatus is incapable of providing so-called focus following operation, that is, continual movement of the primary lens as necessary to maintain it in a focused condition when the object distance is varying. Such capability is required, for example, when the adjusted primary lens is that of a motion picture camera. The incapability of the Biedermann et al. type of apparatus to provide focus following operation stems from the need for returning the mirror and the primary lens of that apparatus to the datum position each time that the lens is to be moved to a new focus position.
The arrangements of the noted Stauffer patents are capable of keeping a primary lens in a focused condition as the object distance varies. However, these arrangements require a rather complex light responsive and signal switching and conditioning or processing means in order to accomplish this operation, the use of which is prohibited in those applications where small size and low cost are mandatory.
A further shortcoming of the known apparatus is its requirement that the primary lens be coupled to and moved along with the auxiliary lens or mirror. Such coupled movement of these elements places a limitation on the speed with which the auxiliary means can be moved or scanned through its range of positions while seeking that position in which correlation is obtained. This limitation is a significant one in some applications.